It is known to support an auxiliary surface, such as may be defined by a keyboard supporting tray, for vertically swinging movement relative to a primary surface, such as may be defined by the top of a table or work station, by a mechanism including a pair of link elements each having first and second ends thereof pivotally connected to an auxiliary surface mounting element or bracket and a primary surface mounting element or bracket, respectively. Such mechanisms typically include a counterbalance spring tending to bias the auxiliary surface mounting element and link elements upwardly relative to the primary surface mounting element, and a manually operable locking mechanism serving to releasably retain the auxiliary surface in a desired vertical position.
It has also been proposed to provide an additional bracket serving to interconnect the auxiliary surface mounting element to the link elements in a manner allowing downwardly directed tilting movement of the auxiliary surface in combination with an additional manually operable locking mechanism serving to releasably retain the auxiliary surface in a desired tilted position.
Known clamping mechanisms are disclosed by U.S. Pat. Nos. 3,908,561; 4,625,657; 4,976,407 and 5,294,087.